An explicit hydrological algorithm for basic flow and transport equations and its application in agro-hydrological models for water and nitrogen dynamics

Hydrological simulation is a key component in argo-hydrological models for optimizing resources use and minimizing the environmental consequences in agriculture. In this study we extended a simple and explicit algorithm for solving the basic soil water flow equation by to the solute transport equation. The key feature of the algorithm is to use a uniform soil layer thickness and a small time step in solving the soil water and solute transport equations, so that the calculations can be made on a layer basis. This drastically simplifies the procedure of modeling water and solute transport in soil using the basic equations. The proposed algorithm was tested against the complex finite element (FE) numerical scheme in simulating soil water and solute transport in different soils via numerical experiments. The results showed that the proposed algorithm with a uniform soil layer thickness of 5 cm and a small time step of 0.001 d was able to achieve the identical accuracy as the FE method. Tests of the proposed algorithm in simulating water and nitrogen dynamics against data from a field experiment on wheat revealed that the predicted results with the simple algorithm were in good agreement with the time-course measurements of soil water and mineral N concentration at the various depths in the profile, suggesting that the proposed algorithm performed well and can be reliably applied in agro-hydrological models. The simplicity and accuracy of the algorithm will encourage scientists to use basic equations for soil water and solute transport more in the future for improving performance of agro-hydrological models.